Fluid metering or transfer rollers, commonly called "anilox rollers," are used extensively in the flexographic printing trade to transfer closely controlled quantities of ink from rubber fountain rollers running in an ink bath to a rubber printing plate roller or cylinder. In turn, the plate cylinder transfers the ink picked up from the anilox roller to a web of material, usually plastic, being printed. The circumferential surfaces of anilox rollers have been engraved with a variety of tiny, closely spaced, shallow depressions called "cells", and the cells retain ink therein when doctor blades scrape the polished surfaces of the rollers otherwise clean of ink.
The most common cells are known as (a) pyramidal, in which the depressions take the shape of inverted four-sided pyramids; (b) quadrangular, in which the depressions take the shape of inverted truncated four-sided pyramids; and (c) tri-helical, in which the depressions are shallow V-grooves extending helically around the circumferential surface of a roller. The pyramidal and quadrangular cells are typically engraved in 45.degree. helical series relative to the roll, criss-crossing to form a diamond pattern of cells. Other shapes and dispositions of cells on the surfaces of anilox rollers (and on other similar rollers used for various coating and printing purposes) have been advanced for various purposes, and U.S. Pat. Nos. 3,613,578, 2,322,530, 4,016,811, 2,393,529, 2,380,047, and 4,009,658 disclose a variety of shapes of cells arranged to form a variety of patterns.
Several problems have existed with previously known anilox rollers, such as (a) moire effects on the web being printed where a regular pattern on the roller falls into some semi-register with a texture pattern of the web, (b) lack of even ink distribution on the web where the ink must bleed across long straight uninked bare streaks or tracks between the ink deposits from the cells, and (c) ink drying and caking in the cells if the cells are deep and irregular enough to reliably hold a full supply of ink when doctor-bladed.
Channel-connected cells, as provided by the present invention, avoid moire effects on the printed web, cause better migration and distribution of ink on the web for evenness of appearance, and are constantly supplied with and reliably hold full supplies of fresh ink when doctor-bladed, to the end that anilox rollers with the channel-connected cells transfer ink with an improved quality, quantity, and consistency not to be found with conventional anilox rollers.